1. Field of the Invention
The present invention relates to a generating method, a creating method, an exposure method, and a storage medium.
2. Description of the Related Art
An exposure apparatus is employed to fabricate semiconductor devices such as a semiconductor memory and a logic circuit using photolithography. The exposure apparatus projects and transfers a pattern formed on an original (a mask or a reticle) onto a substrate such as a wafer by a projection optical system. In recent years, along with advances in micropatterning of semiconductor devices, it has become difficult for an exposure apparatus to transfer (resolve) patterns fine enough to fabricate these devices.
Under the circumstance, so-called multiple exposure is adopted in which a pattern to be formed on a substrate (that is, a geometric pattern corresponding to circuit elements to be integrated on a substrate) is divided into a plurality of patterns, and the divided patterns are transferred by exposure at different times (see U.S. Pat. No. 5,563,012). For example, a double exposure technique called double patterning (DPT) divides a pattern into two patterns, and performs exposure using two masks on which the respective divided patterns are formed. At this time, a pattern is divided such that all pattern elements which form patterns on the respective masks are sufficiently spaced from each other, that is, these intervals between them, which allow the respective pattern elements to individually resolve.
Such a double exposure technique is generally used when a plurality of pattern elements which form a pattern are populated too densely to resolve as individual pattern elements. Note that rule- and model-based decomposition techniques have been proposed to divide a pattern to be formed on a substrate (see U.S. Pat. No. 6,553,562 and Japanese Patent Laid-Open Nos. 2002-287324, 2005-276852, and 2007-183630).
However, the rule-based decomposition techniques require a large number of rules in order to handle complex circuit design. The rule-based decomposition techniques can perform decomposition using a rule set established in advance in order to divide the pattern. Nevertheless, actual circuit design often requires intervention of the user (operator) when a pattern to be formed on a substrate has so complex a two-dimensional geometry that there are patterns (pattern elements) which do not comply with the rules.
The model-based decomposition techniques also suffer from various kinds of problems. For example, the model-based decomposition techniques require a long time to complete the pattern division process. Furthermore, the model-based decomposition techniques often require intervention of the user (operator) because they also suffer from a problem that the pattern cannot be divided depending on circumstances involved.
Also, it is a common practice to use the same illumination condition (effective source) for a plurality of divided patterns without attaching importance to the illumination condition in pattern division. For example, the model-based decomposition techniques generally use a fixed illumination condition for imaging computation. Thus, the model-based decomposition techniques often cannot be used to divide a pattern, such as a pattern in which pattern elements (for example, contact holes) are two-dimensionally arranged. This is because a pattern cannot be resolved by inappropriate illumination condition.
U.S. Pat. No. 6,553,562 discloses a method of dividing a line pattern into a vertical pattern and a horizontal pattern, and using dipole illumination patterns before and after rotation through 90° as the illumination conditions for the respective divided patterns. However, in this case, the illumination condition is merely rotated through 90°, so the illumination conditions before and after the rotation have similar shapes. Also, when pattern division in which adjacent pattern elements are thinned out (that is, the minimum pitch between pattern elements is doubled) is performed instead of dividing the pattern in accordance with its direction, quadrupole illumination or annular illumination is often assumed as the illumination condition, as in Japanese Patent Laid-Open Nos. 2002-287324, 2005-276852, and 2007-183630. In this case as well, identical or similar illumination conditions are used for the respective divided patterns.